* Services sector grows in April, fastest pace in 8 months
* JPMorgan leads banks lower after trading revenue warning
* Pfizer's revenue below expectations, shares fall
* Dow up 0.2 pct, S&P up 0.2 pct, Nasdaq up 0.3 pct (Updates to afternoon)
By Caroline Valetkevitch
NEW YORK, May 5 (Reuters) - U.S. stocks were up slightly on Monday as concerns over an escalation of tensions between Ukraine and pro-Russia separatists were offset by data showing strength in the services sector.
The Institute for Supply Management said its services sector index rose in April, hitting the fastest pace in eight months and topping expectations.
Shares had opened lower, weighed by geopolitical events as Ukrainian forces were ambushed by separatists on Monday, triggering heavy fighting on the outskirts of the rebel stronghold of Slaviansk, a day after a Ukrainian police station in Odessa was stormed.
"We shook off a lot of the morning jitters, and the ISM services came out and showed pretty good growth, and that obviously brought back some buyers," said Ryan Detrick, senior technical strategist at Schaeffer's Investment Research in Cincinnati, Ohio.
Still, bank shares were under pressure as JPMorgan Chase fell 2.7 percent to $54.10. The bank said late on Friday it expects second-quarter revenue from bond and equity trading to decline by about 20 percent from a year earlier. The S&P financial index fell 0.5 percent.
The Dow Jones industrial average rose 25.4 points or 0.15 percent, to 16,538.29, the S&P 500 gained 3.6 points or 0.19 percent, to 1,884.74 and the Nasdaq Composite added 12.957 points or 0.31 percent, to 4,136.854.
Energy shares were among the best performers, with the S&P energy index up 0.5 percent.
Occidental Petroleum, the fourth-largest U.S. oil and gas company, reported a better-than-expected profit for the third straight quarter, helped by higher prices for crude oil and natural gas in the United States. Shares rose 0.5 percent to $94.93.
Pfizer Inc also lost ground. The biggest U.S. drugmaker reported revenues well below analysts' expectations. Shares fell 2.7 percent to $29.93.
Target Corp shares fell 3.2 percent to $60.05 after news that Chief Executive and Chairman Gregg Steinhafel will leave the company in the wake of a data breach late last year that hurt profits, shook customer confidence in the No. 3 U.S. retailer and prompted congressional hearings.
German aircraft seating maker Recaro said it was studying the possibility of buying assets from B/E Aerospace after the U.S. company announced a surprise review. B/E Aerospace shares jumped 10.7 percent to $98.46. (Additional reporting by Chuck Mikolajczak; Editing by Bernadette Baum and Nick Zieminski)